In a multiprotocol label switching (MPLS) network, a signaling protocol may be used to set up a label switched path (LSP) in the MPLS network. MPLS may permit a network to direct a flow of packets along a predetermined path (e.g., a LSP) across the network. As part of setting up the LSP, label switching routers (LSRs) included in the MPLS network may set up a label information base (LIB) that maps an incoming label from an input port of the LSR to an output port of the LSR and to a new label value. The LSRs may forward packets along links through the MPLS network based on labels attached to the packets that indicate which LSP to use. The label may be swapped to the new label at each router hop. In this way, a LSP may identify the specific path of nodes (e.g., routers) and links that the packets take through the MPLS network.
Resource reservation protocol (RSVP) may be used to reserve resources across a network. RSVP may be used by either a host or a router to request or deliver specific qualities of services (QoS) for application data streams or flows. RSVP may define how applications place reservations and how they may relinquish the reserved resources once the need for them has ended. In RSVP LSPs, various protection mechanisms can be used to protect against link and node failures. These failure mechanisms may construct a bypass tunnel across a protected link/node. Generally, the bypass tunnel gets used only in case of failure.
Software utilities, such as LSP ping and LSP traceroute utilities, are useful tools for identifying failed connectivity between two nodes in an MPLS network. These tools typically require a user to enter a unique identifier, such as a particular internet protocol (IP) address, of a remote host in order to test the connectivity to that remote host over an LSP. For example, an LSP ping may test connectivity to a remote host by sending an MPLS echo request packet to a specific IP address to test the status of connectivity to a particular target device having the IP address. If an echo reply packet is not received within a defined time period, connectivity to that device is assumed to be down.
Similarly, an LSP trace may require an IP address for a target device in order to test connectivity from the source device to that target device. The LSP traceroute utility may test connectivity to the remote target device by tracing an MPLS echo request packet's path from the source device to the particular IP address specified by the user. As output, the LSP trace may show how many hops the packet traveled to reach the IP address, identify each hop by its IP address, and show the amount of time each hop took.